Electric discharge lamp having a resiliently suspended fragile member therein that decreases the diffusion length of the discharge



Apnl 2, 1968 A w. WAINIO 3,376,456

ELECTRIC DISCHARGE LAMP HAVING A RESILJIENTLY SUSPENDED FRAGILE MEMBER THEREIN THAT DECREASES THE DIFFUSION LENGTH OF THE DISCHARGE Filed Nov. 5, 1964 FIG.|.

INVENTOR Albert W Woinio 3,376,456 ELECTRIC DISCHARGE LAMP HAVING A RE- SILIENTLY SUSPENDED FRAGHLE MEMBER THEREIN THAT DECREASES THE DHFFUSION LENGTH OF THE DISCHARGE Albert W. Wainio, Livingston, N.J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 5, 1964, Ser. No. 409,246 7 Claims. (Cl. 313-204) This invention relates generally to electric discharge lamps and has particular reference to high-output fluorescent lamps and means for suspending an elongated member therein.

In order to reduce lighting costs various types of high-output fluorescent lamps have recently been developed. The major obstacle in the design of such lamps is the inherent tendency of the lamp etliciency to decrease as the power input and current density within the gaseous discharge are increased. When the current loading increases the electron temperature decreases resulting in a decrease in efiiciency of generation of 2537 A. radiation within the discharge and a corresponding drop in the relative light output.

One approach to this problem is to place an elongated member within the lamp that extends along the discharge space and defines a recombination surface for the electrons and positive ions in the plasma and thus effectively decreases the ditiusion length of the discharge. The elongated member may be a glass rod or the like that is coaxially mounted within the lamp and is so dimensioned that it does not materially decrease the crosssectional area of the discharge space defined by the envelope or interfere with the free passage of the discharge through the lamp.

The reduction in the diffusion length of the discharge produced by the rod increases the electron temperature and thus maintains the efl'iciency of the lamp at high power loadings within acceptable limits without locally increasing the current loading per unit of cross-sectional area of the discharge. A high-output fluorescent lamp embodying these principles is described in detail and claimed in copending application Ser. No. 112,071 now Patent No. 3,290,538 of Daniel A. Larson et al., filed May 23, 1961, and assigned to the assignee of the present invention.

In order for maximum light output and efliciency to be obtained it is necessary that the glass rod be located precisely at the axis of the envelope and extend for practically the entire length of the discharge path. In addition, the rod must have a small cross-section relative to that of the envelope in order to avoid constricting the discharge and increasing the current density per unit of cross-sectional area. The rod is thus inherently very fragile and, if rigidly mounted, will break should the finished lamp be subjected to severe mechanical impacts during shipment or subsequent handling. Last but not least, the rod must be suspended in the desired position within the lamp envelope by support means which will not materially obstruct the discharge, mask large areas of the bulb wall or require radical departures from standard lampmaking practice.

It is, accordingly, the general object of the present invention to provide an improved electric discharge lamp which contains a fragile elongated member and will withstand the mechanical shocks and stresses normally encountered during handling and shipping.

Another and more specific object is the provision of an improved highly-loaded fluorescent lamp which contains an internally mounted glass rod and can be conveniently and quickly assembled.

States Patent Patented Apr. 2, 1968 A further object is the provision of a rugged support structure for resiliently mounting a fragile elongated member in a predetermined position within a lamp envelope without materially obstructing the latter.

The foregoing objects, and other advantages which will become apparent as the description proceeds, are achieved in accordance with the present invention by suspending the glass rod (or other member) in the desired position within the discharge space by means of a plurality of spaced pier-like supports that are attached directly to the inner surface of the envelope. Specifically, each of the support structures comprise a stud of cane glass and a resilient tie wire having one end embedded in the glass stud and its opposite end bent into an expandable loop that is shaped to receive an compressively grip the glass rod when the latter is forcibly inserted therein. The glass studs are sealed directly to the envelope wall and preferably are shaped to permit the tie wires to flex without chipping the glass. The glass rod is thus spring mounted within the envelope by virtue of the shock-absorbing action of the tie wires and is protected from breakage under normal handling conditions.

A better understanding of the invention will be obtained by referring to the accompanying drawings, wherein:

FIGURE 1 is an elevational fragmentary view of a high-output fluorescent lamp embodying the rod supporting structure of the present invention, portions of the envelope being omitted for convenience of illustration;

FIG. 2 is an enlarged cross-sectional view through the lamp along the line IIII of FIG. 2; and,

FIGS. 3 and 4 are elevational views of alternative forms of support structures according to the invention.

With specific reference to the drawings, in FIG. 1 there is shown a highly-loaded fluorescent lamp 10 which incorporates the present invention and consists of a tubular light-transmitting envelope 12 having a coating .14 of suitable ultraviolet-responsive fluorescent phosphor on its inner surface. A glass stem 16 is sealed into each end of the envelope and a predetermined quatity of mercury and a suitable fill gas, such as argon or a mixture of neon and argon at from 1 to 4 millimeters pressure for example, are introduced into the envelope in accordance with standard lampmaking practice. A pair of lead wires 17 and 18 are sealed through each of the stems 16 and the inner ends of the lead wires are attached, as by clamping, to a suitable electrode structure 20, such as a coiled tungsten filament that is coated with suitable emission material. The outer ends of the lead wires are connected to a pair of pins 24 carried by a base member 22 that is fastened to the respective ends of the envelope 12.

In order to control the mercury vapor pressure within the lamp when the latter is energized, a heat shield 21 of aluminum or the like may be attached to each of the stems 16 to provide a relatively cool chamber at each end of the lamp in which the mercury vapor can condense. A suitable elongated member such as a slender glass rod 26 of substantially circular and uniform cross-section is suspended in a predetermined portion of the discharge space between the electrodes 29 and in longitudinally extending relationship with the envelope 12 and the discharge path in accordance with the inventive concept disclosed in the aforementioned copending Larson et al. application. Preferably, the glass rod 26 is suspended in coaxial relationship with the envelope between the electrodes and has a diameter less than that of the envelope.

T he invention The present invention is directed to the problem of suspending the glass rod 26 in the desired position within the envelope 12 and the improved support structure by which this is achieved will now be described.

'As is shown in FIGS. 1 and 2, the glass rod 26 is centrally suspended within the discharge space by a plurality of spaced support structures 30 that are attached to the inner surface of the envelope 12 and extend radially therefrom toward the envelope axis. Each of the support structures 30 consists of a tie wire 32 having a substantially straight end 33 that is embedded in a preformed body of vitreous material such as a glass stud 34 that is sealed directly to the inner surface of the envelope 12. The opposite end of the tie Wire is bent into an expandable clasp such as a generally U-shaped loop 35 that encircles and is mechanically interlocked with the glass rod 26.

As shown in FIG. 2, the tips of the straight end portions 33 of the tie wires 32 are preferably flattened to provide spade-like enlargements 40 that firmly anchor the wire in the respective studs 34.

The supports 30 are preferably located on the same side of the rod 26 and the small indents 13 formed when the envelope is sealed to the studs are disposed in substantially a straight line along one side of the envelope, as shown in FIG. 1. In the case of a 96 inch fluorescent lamp having an envelope 2 inches in diameter and a rod /s inch in diameter approximately 82 inches long, six support structures 30 are preferably used and are spaced approximately 14 inches apart and 6 inches from the ends of the rod. To facilitate rod alignment and avoid severe expansion stresses during bulb lehring and subsequent lamp operation, it is desirable in the aforesaid 8 foot lamps to use two axially aligned rods that are approximately 42 inches long and held in place by three evenly spaced support structures. Additional advantages in this regard can be obtained by using three rods approximately 27% inches long and two supports per rod spaced about 7 inches from the respective ends of the rod. In the case of 48 inch lamps a single rod about 40 inches long can be used with three or four uniformly spaced support structures.

As shown more particularly in FIG. 2, the bend of the U-sharped loop 35 has the same curvature as the rod 26 so that the latter is nestingly seated therein. The loop is than the diameter of the rod. The tie wire is fabricated also so dimensioned that it defines an opening slightly less from the metal such as nickel plated iron that is relatively stiff and resilient and will retain its resiliency at the temperatures which prevail within the envelope during bulb lehring and subsequent operation of the finished lamp. Satisfactory results have been obtained by fabricating it from nickel-plated steel wire commonly referred to in the art as piano wire. The loop 35 is thus resiliently expandable and compressively grips the glass rod 26 when the latter is forcibly inserted therein.

*As is illustrated in FIG. 2, the end of the glass stud 34 at the juncture with the embedded end 33 of the tie wire 32 is tapered inwardly and defines a reentrant coneshaped recess or cavity 37 that extends around the base of the wire. This is an important feature of the invention since it permits the exposed ends of the tie wires and the rod to flex as a unit in a lateral direction relative to the longitudinal axis of the supports 30 without touching or chipping the end of the glass studs. It has been found that the aforesaid cavity is formed automatically when the flattened end of the tie wire is pushed into the headsoftened end of the glass stud during the assembly of these members.

As is shown in FIG. 1 and more particularly in FIG. 2, the glass rod 26 is coated with a layer 28 of phosphor or, if desired, with a suit-able material such as magnesium oxide that will reflect the ultraviolet radiations generated by the discharge and direct them back onto the phosphor coating 14 on the envelope 12.

Assembly In fabricating the lamp the support structures 30 are first assembled and then fastened to the coated glass aligned with one another so that I rod 26. Since the coating 28 at this point is dry and still contains the organic binder, such as nitrocellulose, customarily used in applying the phosphor to the lamp envelope, the rod can be handled and clamped into the tie wire loops 35 Without damaging or removing the coating. During the bulb lehring operation the binder is decomposed in the usual manner leaving the desired powderlike coating of phosphor, or magnesium oxide or other material which is used.

The assembled rod 26 and support structures 30 are then placed in a suitable fixture which is inserted into the coated envelope 12 and oriented therein so that the rod is disposed at substantially the axis of the envelope.

The overall length of each of the support structures 30 is such that the ends of the glass studs 34 lie adjacent the inner surface of the envelope when the rod is thus positioned. The portions of the envelope overlying the ends of the studs are then heated, as by suitably located gas burners, until the glass softens and collapses inwardly into sealing relationship with the ends of the studs.

After the glass has cooled and solidified, the envelope is placed in an oven and lehred to decompose and vaporize the organic binder material. The stems 16 are then sealed into the ends of the envelope and the other operations required to complete the lamp are carried out in the regular fashion.

If desired, the envelope and rod can both be coated by flushing the phosphor paint into the envelope in the well known manner after the rod has been mounted therein. In this case, both the rod 26 and the support structures 30 will be coated with phosphor.

The flexibility of the tie wires provides an additional advantage in lamp manufacturing in that they automatically compensate for any differences in expansion that may occur between the rod and envelope during bulb lehring, or when the finished lamp warms up to its operating temperature.

Alternative embodiments In FIG. 3 there is shown another form of support structure 30a wherein the end of the tie wire 32a is bent into a closed loop 35a of substantially circular .config ur-ation that is terminated by a tangentially extending pig-tail 36. Insertion and clamping of the coated rod 26a within the loop 35a is accomplished in this case by pressing the pig-tail 36 against the shank 33a of the tie wire to temporarily expand the loop and thereby allow the rod to be threaded through and properly positioned therein.

In FIG. 4 there is shown still another form of support structure 30b wherein an intermediate segment of the.

Test results Comparative tests conducted on 96 inch fluorescent lamps having envelopes 2% inches in diameter and containing three glass rod inch in diameter and 27% inches long mounted coaxially within the envelopes in accordance with this invention have Shown that such lamps will withstand a 4 foot drop onto a hard surface without rod breakage. On the other hand, a lamp of the same size and type having a nseries of A; inch diameter rods 7 inches long with one end rigidly secured to envelope wall developed broken l'ods when droppedthrough a distance of only 2 feet under identical condtions.

It will be appreciated from the foregoing that the objects of the invention have been achieved in that there has been provided a fluorescent lamp having a fragile elongated member suspended therein which displays surprising strength under impact and can be readily mounted in the lamp during the regular sequence of manufacturing operations.

While several embodiments of the invention have been illustrated and described, it will be appreciated that various changes in both the configuration and arrangement of the various parts can be made without departing from the spirit and scope of the invention. For example, the tie wires need not be anchored in glass studs as above described but may be embedded in nodular shaped elements that are fastened to, or actually constitute part of, the envelope wall.

The loops formed on the ends of the tie wires 32 can also be of any configuration. For example, the end of the tie wire can be bent to form a pair of conjoined U- shaped loops that are arranged in tandem relationship and dimensioned to mechanically interlock with and grip a longer segment of the rod. Care should be taken in each case, however, to keep the length of the tie wire greater than that of the vitreous body in which it is anchored to enable the tie wire and rod to flex as a unit when the lamp is subjected to severe vibration or mechanical impacts.

I claim as my invention:

1. In an electric discharge lamp having an envelope that contains an ionizable medium and a pair of spaced electrodes operable when energized to sustain an electric discharge therebetween, the improvement comprising the combination of a fragile elongated member disposed in the discharge spaced between said electrodes, and

means suspending said elongated member within said envelope at a predetermined location in the discharge space and in longitudinally extending relationship with the discharge path between said electrodes comprising (1) a pair of spaced nodular elements that are integral with and project transversely from the side wall of said envelope into the discharge space and (2) a corresponding number of resilient tie wires that are anchored in the respective nodular elements and have their free ends formed into expandable clasps that compressively grip and are mechanically interlocked with said elongated member,

said nodular elements being so spaced that the expandable clasp portions of the respective tie wires grip preselected intermediate portions of the elongated member that are disposed inwardly from the ends of said member.

2. In a fluorescent lamp having an elongated vitreous envelope that contains an ionizable medium and is interiorly coated with phosphor, the improvement comprising the combination of:

a pair of spaced electrodes sealed Within said envelope and operable when energized to sustain an electric discharge therebetween,

a fragile elongated vitreous member of substantially uniform cross-section disposed between said electrodes, and

a plurality of spaced elongated supporting structures suspending said vitreous member within said envelope at a predetermined location in the discharge space and in longitudinally extending relationship with the discharge path between said electrodes,

each of said support structures comprising (1) a vitreous stud that is sealed to and projects transversely from the inner surface of said envelope into the discharge space and (2) a resilient tie wire having one end embedded in said vitreous stud and its oppositte end formed into an expandable loop that is clamped around and compressively grips a portion of said elongated member, the respective stud and the tie wire structures being spaced predetermined distances from each other and the respective ends of said vitreous member.

3. The combination set forth in claim 2 wherein an intermediate portion of each of said resilient tie wires is bowed in a direction transverse to the axis of the respective support structures and is thereby adapted to serve as a shock-absorbing means.

4. In a high-output fluorescent lamp having a tubular glass envelope that contains an ionizable medium and has a phosphor coating on its inner surface, the improve ment comprising the combination of:

a pair of spaced electrodes sealed into the ends of said envelope and operable when energized to sustain an electric discharge therebetween,

a slender glass rod of substantially uniform and circular cross-section disposed between said electrodes and extending along substantially the entire length of the discharge path, and

a plurality of spaced support structures holding said glass rod in substantially coaxial relationship with said envelope,

each of said support structures comprising (1) a glass stud that is sealed to the inner surface of said envelope and projects radially inwardly therefrom toward the envelope axis and (2) a resilient tie having one end embedded in said glass stud and its opposite end formed into an expandable p that is clamped around and compressively grips a preselected intermediate portion of said rod,

the exposed portion of said tie Wire having a length greater than said stud and sufiicient to enable the tie wire to fiex and cushion mechanical shocks that would otherwise be imparted to the glass rod from the envelope.

5. A support structure for suspending a fragile elongated member in a predetermined location and longitudinally extending relationship within a gaseous discharge device comprising:

a body of vitreous material, and

a resilient tie wire having (1) a substantially straight end portion that is embedded in said vitreous body and (2) an expandable loop at its opposite end that is dimensioned and contoured to nestingly receive and compressively grip a predetermined portion of said elongated member,

the surface of said vitreous body at the juncture thereof with said tie wire being tapered and defining a reentrant substantially cone-shaped crevice that permits the exposed portion of said tie wire to flex without contacting said vitreous body.

6. The support structure set forth in claim 5 wherein; said loop is of generally U-shaped configuration and the end of the tie wire embedded in said vitreous body is enlarged in a transverse direction.

7. The support structure set forth in claim 5 wherein; said loop is of generally circular configuration and is terminated by a tangentially extending pig-tail, and the end of the tie wire embedded in said vitreous body is enlarged in a transverse direction.

wire

References Cited UNITED STATES PATENTS 1,933,941 11/1933 Taylor l7428 3,145,320 8/1964 Nicolaro 3l3-286 3,160,775 12/1964 Plagge 3l3109 3,290,538 12/1966 Larson et al 3l3l09 JAMES W. LAWRENCE, Primary Examiner. ROBERT SEGAL, Examiner. R. JUDD, Assistant Examiner. 

1. IN AN ELECTRIC DISCHARGE LAMP HAVING AN ENVELOPE THAT CONTAINS AN IONIZABLE MEDIUM AND A PAIR OF SPACED ELECTRODES OPERABLE WHEN ENERGIZED TO SUSTAIN AN ELECTRIC DISCHARGE THEREBETWEEN, THE IMPROVEMENT COMPRISING THE COMBINATION OF: A FRAGILE ELONGATED MEMBER DISPOSED IN THE DISCHARGE SPACED BETWEEN SAID ELECTRODES, AND MEANS SUSPENDING SAID ELONGATED MEMBER WITHIN SAID ENVELOPE AT A PREDETERMINED LOCATION IN THE DISCHARGE SPACE AND IN LONGITUDINALLY EXTENDING RELATIONSHIP WITH THE DISCHARGE PATH BETWEEN SAID ELECTRODES COMPRISING (1) A PAIR OF SPACED NODULAR ELEMENTS THAT ARE INTEGRAL WITH AND PROJECT TRANSVERSELY FROM THE SIDE WALL OF SAID ENVELOPE INTO THE DISCHARGE SPACE AND (2) A CORRESPONDING NUMBER OF RESILIENT TIE WIRES THAT ARE ANCHORED IN THE RESPECTIVE NODULAR ELEMENTS AND HAVE THEIR FREE ENDS FORMED INTO EXPANDABLE CLASPS THAT COMPRESSIVELY GRIP AND ARE MECHANICALLY INTERLOCKED WITH SAID ELONGATED MEMBER, SAID NODULAR ELEMENTS BEING SO SPACED THAT THE EXPANDABLE CLASP PORTIONS OF THE RESPECTIVE TIE WIRES GRIP PRESELECTED INTERMEDIATE PORTIONS OF THE ELONGATED MEMBER THAT ARE DISPOSED INWARDLY FROM THE ENDS OF SAID MEMBER. 